1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking electrolyte electrode assemblies and separators alternately. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes. The fuel cell stack is installed in a vehicle.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which comprises two electrodes (anode and cathode) and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane (proton exchange membrane). The membrane electrode assembly is interposed between separators.
The membrane electrode assembly and the separators make up a unit of a fuel cell (unit cell) for generating electricity. Typically, a predetermined number of membrane electrode assemblies and separators are connected together to form a fuel cell stack. In the fuel cell stack, a fuel gas such as a hydrogen-containing gas is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane which is appropriately humidified, and the electrons flow through an external circuit to the cathode, creating a DC electric current. An oxygen-containing gas or air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
U.S. Pat. No. 5,662,184 (prior art 1) discloses a type of the fuel cell stack for use in a vehicle. As shown in FIG. 18, in the prior art 1, a fuel cell system is installed in a front box 2 of the vehicle 1. A radiator 3 is provided at a front region in the front box 2 of the vehicle 1. Outside a vehicle frame 4, front wheels 5 are rotatably attached to opposite ends of a front axle 6. A motor 7 is driven to rotate the front axle 6. A pair of fuel cell stacks 8 are provided inside the vehicle frame 4 for supplying electricity to the motor 7. A compressor 9 for supplying an oxygen-containing gas is interposed between the fuel cell stacks 8. Though not illustrated, components such as fuel tanks, a reformer, and a compressor for supplying a fuel gas are provided in a rear region (on the side of a trunk) of the vehicle 1. Each of the fuel cell stacks 8 includes a plurality of unit cells 8a stacked in a horizontal direction indicated by an arrow X.
If the fuel cell stacks 8 are attempted to be installed in a vehicle of a different type, the space for installation may be different. Therefore, the arrangement of the unit cells 8a such as the shape of the electrodes of the unit cells 8a, and the dimensions of reactant gas passages need to be designed again. Further, the position for installing the fuel cell stack 8 often changes depending on the type of the vehicle. For example, the fuel cell stack 8 may be installed under the vehicle floor, in the front box, in the trunk box, or in the ceiling region of the vehicle. When the installation position changes, installation conditions such as the shape and dimensions of the space for installing the fuel cell stack 8 may be different.
Therefore, various designs of dedicated fuel cell stacks 8 are needed for the different installation positions, i.e., to meet the different installation conditions in the various types of vehicles. The expense for the different designs, and the factory equipment cost for producing the different fuel cell stacks 8 are high.
In an attempt to address the problem, for example, Japanese Laid-Open patent publication 11-67259 (prior art 2) discloses a stack structure for a fuel cell having an inner manifold type separator in which each of an electrode part and a manifold part has a square shape. With the structure, a plurality of the fuel cells are arranged easily adjacent to each other in a horizontal direction or a vertical direction.
However, the prior art 2 merely discloses the electrode part and the manifold part having a square shape, and the fuel cell stack may not be used practically in the vehicle application. When a plurality of fuel cell stacks are arranged adjacent to each other laterally, for example, the overall dimension of the fuel cell stacks in the lateral direction may be too large. The surface area of the electrodes of the unit cell may be small. In this case, a large number of unit cells need to be stacked for obtaining a high power output. Therefore, the dimension in the stacking direction of the unit cells is large, and the fuel cell stack can not be installed effectively in different positions in various types of vehicles, i.e., in spaces having different sizes and shapes.